1. Field of the Invention
The present invention relates to a scanning probe microscopy used for, e.g., a surface measuring apparatus, a surface treatment apparatus, and a surface processing apparatus.
2. Description of the Related Art
A scanning tunneling microscopy (to be referred to as an STM hereinafter) has been developed as a device for observing each atom on the surface of a solid one by one. A conductive probe having a sharp tip scans the surface of a conductive sample in STM. The STM is designed to measure the structure of the sample surface at the atomic level by measuring a tunnel current flowing between the sample and the probe during scanning. Since the STM performs measurement by using a tunnel current flowing between a sample and the probe, the STM can be applied to only conductive samples. Recently, however, a microscope capable of measuring the surface of an electrically insulating sample has been developed by utilizing the technology of STMs. This microscopy is called an atomic force microscopy (to be referred to an AFM hereinafter), which is designed such that a probe is supported by a cantilever, and the displacement of the cantilever caused by a force acting between a sample surface and the probe is measured by using the principle of STMs, thereby measuring the structure of the sample surface. Similar to the STM, the AFM can three-dimensionally measure the shape (structure) of a sample surface by measuring the displacement of the cantilever while scanning the sample surface using the probe.
STMs and AFMs can be applied not only to measurement of sample surfaces but also to processing apparatuses and surface treatment apparatuses. If, for example, they are applied to processing apparatuses, the probe is moved to a desired position on a surface after a sample structure is measured, and a pulse voltage is applied between the prove and the sample to perform atomic-scale microscopic processing under the probe. In addition, by causing the probe to collide with a sample surface, a microscopic uneven pattern can be formed on the sample surface. In the application of STMs and AFMs to surface treatment apparatuses, if gaseous or liquid molecules are present between the probe and a sample, the molecules are attracted to or repelled from the sample by an electric field generated by an applied voltage.
In the above-described STM or AFM, the surface of a sample must be scanned by the probe. A so-called scanning probe microscopy for realizing such a scanning operation is generally constituted by a ga length control system for keeping the gap length between the probe and the sample constant, and a scanning system for causing the probe to scan the surface of the sample by moving the probe and sample relative to each other in a direction along the sample surface.
The gap length control system of the conventional scanning probe microscopy is designed to drive a Z-axis direction driving piezoelectric element so as to keep a tunnel current flowing between a sample and the probe constant, i.e., keep the gap length between the sample and the probe constant, and extract an input signal to an amplifier as an observation signal. If, therefore, an uneven pattern of the atomic level is formed on the surface of the sample, the observation signal changes in accordance with the uneven pattern. The surface structure of the sample can be determined in accordance with the changes in observation signal.
The following problems, however, are posed in the conventional scanning probe microscopy. The surface of a sample is not necessarily parallel to the X-Y plane but is often inclined therefrom at a certain angle. For this reason, in order to measure an uneven pattern on the surface of a sample throughout a wide range of the surface, a piezoelectric element having a large expansion/contraction amount is required. Therefore, a high-voltage amplifier is used to satisfy the above requirement. In general, however, a high-voltage amplifier has a low response speed (i.e., a large time constant) and produces large noise.
In the above-described STM, since the scanning speed is determined by the tracking speed of the Z-axis driving piezoelectric element and an electrical amplification time, scanning requires several minutes per frame (=100 .ANG..times.100 .ANG.). In addition, if high-speed scanning is forcibly performed, although the apparatus can roughly respond to the height and depth of a sample, it is difficult to observe a fine uneven surface.
As described above, in the conventional scanning probe microscopy, the upper limit of the scanning speed at which the probe can scan the surface of a sample is determined by the driving time constant of the gap length control system for driving the piezoelectric element, especially the response speed of the high-voltage amplifier for applying a voltage to the piezoelectric element. For this reason, the scanning speed cannot be essentially increased. The problem of low scanning speed causes various inconveniences. In many cases, the surface structure of a sample changes with the lapse of time. If, therefore, the conventional scanning probe microscopy is used, a surface structure which changes with the lapse of time cannot be measured in a real-time manner. The performance of a scanning probe microscopy and the like is determined by the speed at which a sample surface can be scanned. Similarly, in surface processing, the performance of an apparatus is determined by the speed at which microscopic surface processing can be performed.
In order to eliminate the above-described inconvenience, it may be required that a high-speed, high-voltage amplifier having small noise and a high response speed be manufactured. The realization of the high-speed, high-voltage amplifier accompanies technical difficulty and inevitably causes an increase in cost.
As described above, since the scanning speed of the conventional scanning probe microscopy cannot be increased, the microscopy cannot be applied to high-speed measurement, processing, treatment, and processing.
In another method, an image of a measured portion is formed by detecting changes in tunnel current. This method, however, cannot respond well to large inclinations and a rough uneven pattern on the surface of a sample and the probe may inadvertently collide with the sample surface.
In addition, when a sample is to be measured while it is heated, deformation and the like of the sample due to heat may be caused. Therefore, an increase in speed of scanning is required.
The techniques associated with the present invention are disclosed in Published Unexamined Japanese Patent Application Nos. 1-206202 and 2-275350 and G. Binnig and H. Rohor, "SCANNING TUNNELING MICROSCOPY", IBM Zurich Research Laboratory, CH-88003 Ruschlikon, Switzerlar, Sept. 25, 1987, pp. 236-244.